Background: A national cross-sectional survey on the reporting of critical values was conducted to provide suggestions on monitoring of the quality indicator and obtain the goal of quality improvement. Methods: All clinical laboratories participating in the external quality assessment (EQA) programs of chemistry, blood gas, and hematology tests organized by the National Center for Clinical Laboratories (NCCL) were enrolled in our study. General information on the policy of critical values reporting and the particular problems about critical limits and practice of critical values reporting in the last 2 months were asked in the questionnaire. All collected data were analyzed by the special statistical software designed by the NCCL. Results: The return rate of surveys for critical values on clinical biochemistry, blood gas, and hematology testing were 46.11%, 41.14%, and 39.42%, respectively. Most laboratories in the surveys suggested they set different critical limits for children and adults. The analytes of critical values chosen most frequently were potassium, glucose, sodium, calcium, pH, pCO 2 , pO 2 , white blood cell (WBC) count, hemoglobin (Hb), prothrombin time (PT), activated partial thromboplastin time, and fibrinogen. The analytes with most critical values were potassium, blood gas, and creatinine for clinical biochemistry, pCO 2 for blood gas, and WBC, Hb, and PT for hematology testing. The medians of critical limits for potassium, sodium, calcium, and glucose were not significantly different from the results of the national survey conducted by Kost in 1990. Conclusions: Remarkable inter-laboratory difference in the development and implementation of critical values reporting procedure were found. Laboratories should communicate with clinicians to obtain consensus on the analytes and limits of critical values.